Brazing alloy



` Patented May 22, v1.945

BRAZIN G ALLOY Walter A. Dean, Lakewood, Ollio, assignor to v 'AluminumCompany of America, Pittsburgh, Pa., a corporation of Pennsylvania NoDrawing. Application June 19, 1943; Serial No. 491,559

3 Claims. (Cl. 75-173) This invention relates to` filler metal alloys tobe used `in the fusion joining of metal members, and it is moreparticularly concerned with the Iprovision of a ller metal compositionadapted for brazing aluminum and aluminum base alloy members. v

One of the common methods of joining metal members is to fuse anothermetal of lower melting .point between the abutting edges or faces of themembers being joined and rallow the metal to solidify, thus establishinga rigid metallic bond between the members. The joining of metal membersin this manner is here referred to as fusion joining. 'I'he types offusion joining are such alloys at solution heat treating temperaturesbecause the filler metal would run away from the joint where the jointhad been made previous t solution heat treatment or if, ajointing wereattempted during this thermal treatment. 'I'o` use such a low meltingfiller metal in making a joint on materialwhich has received a solutionheat treatment and has been cooled to room temperature would vitiate thebenefits gained from the4 solution heat treatment, at least in theneighbory hood of the joint. 'I'hese drawbacks are especially evident infurnace brazing practice. It would be advantageous therefore, to have-afiller metal -Which melts above 800 F. but below 1000 F: and

generallyclassied according to the temperature l5 thus permit combiningthe brazing and solution range within which the operation is conducted.heat treating operations; however, no known Soft soldering is carriedout in a relatively low satisfactory filler metal has been available fortemperature range, usually below about 500 F., making joints within theaforesaid temperature` Without fusion of the members being joined.range. Brazing is done at a somewhat higher tempera- In brazing metalmembers it is necessary that ture and generally without fusion of any ofthe the filler metal should have a melting point close A metal members.In contrast to the two precedto the temperatur'eat which the brazing isdone ing practices, welding is performed at a still in order to obtain arigid structure shortly after higher temperature and a very smallportion of the brazed assembly has vbeen withdrawn from the metalmembers is actually fused at the edges -theheating medium. The use of asoft solder or of the joint. In all three methods a flux is 'genesimilar low melting point alloy as a filler `metal erally preferred forthe dual purpose of remov. in place of the higher melting point fillermetals ing superficial oxide lms or other non-metallic mentionedhereinafter has certain inherent disimpurities and promoting the spreadof the fused advantages in addition to those mentioned above y metal.Because of the diierence in the temregarding filler vmetals meltingbelow 800 F. perature ranges at which these various joining Among themost important of these disadvantages operations are conducted, diierenttechniques are is the fact that the filler metal remains molten followedin effecting a joint.- 'over a substantial temperature interval when theThe brazing of aluminum and aluminum base fbrazed assembly is cooled toroom temperature valloys is a comparatively recentdevelopmentfbeafter'removal from the brazing furnace or other cause ofthe difliculty of removing the oxide heating means. If such an assemblyis chilled,v film on the surfaceof the aluminum.v A further thefused,1ler metal may crack as it freezes, diiiiculty arises in thebrazing of agehardening thus making an unsound-joint, or even no joint paluminum base alloys which receive solution and at all, that is, themembers of the assembly may subsequent age hardening treatments todevelop 40 not even adhere to each other. Furthermore, their maximumtensile strength and hardness bethe fact that the joint doesnot becomerigid imcause brazing of such alloys must be done within mediately uponcooling from the brazing temthe solution heat treating temperature rangeof perature permits some displacement ofthe memabout 800 to 1000 F. andgenerally below the tem-` bers and misalignment with respect toeachother. perature of lincipient fusion of any of the con- In 'extremecases, the members might actually Astituents of-the alloy if adverseeiects of overbecome separated. It is therefore apparent that heatingare to be avoided. Brazing these alloys it is highly desirable; if notimperative, that a above about 1000 F. generally causes marked infillermetal be employed which has a melting cipient fusion of 4sorne of theirconstituents with point close tothe brazing temperature. consequent lossin strength and resistance to -cor' 50 It is an object. o f my inventionto provide a rosion as well as softening the metal to the point fillermetal'for brazing which has a melting point where undesirable distortionoccurs. On the below a temperature of about 1000 F. but above otherhand, even if a suitable filler metal were l 800 F. Another object is toprovide a iiller available having a melting point below 800 F. it metalmelting below 1000 F. which is especially still-would not be possible tosatisfactorily braze adapted to form a brazed joint between members ofaluminum or ular object is aluminum base alloys. A particto provide abrazing alloy filler metal which can be employed to form a joint duringthe solution heat treatment of assembled age hardening aluminum basealloy members.

I have discovered that alloys melting below l000 F. .which contain fromabout 56 to 70 per cent silver and 21 to 31 per cent aluminum in theproportion of approximately l part of aluminum to between 2 and 3 partsof silver, and from 7 to 16 per cent copper form an excellent fillermetal for brazing purposes, especially in furnace brazing. These alloysare characterized by having a melting point between about 900 and 1000F. and possessing an adequate strength for holding structural memberstogether under operating conditions. They are especially useful inform-v ing brazed joints between members of aluminum base alloys, andmore particularly, members of heat treatable aluminum base alloys. In mypreper cent silicon,

ferred practice I employ from about 62 to 65 per cent silver, 26 to 27per cent aluminum in the proportion of 1 part of aluminum to 2.a partsof silver, and 8 to 12 per cent copper. In choosing an alloy for brazinga particular heat treatable aluminum base alloy, it is generallydesirable to select a composition that melts at or slightly below thetemperature normally employed for solution heat treatment.

To enhance certain characteristics of the foregoing alloys and to assistin obtaining melting points in the lower portion of the 900 to 1000 F.range, it is desirable at times to include the additional elementsantimony, lead, tin, and bismuth. For the purpose of my invention theseelements are considered as constitutingv a group of metals because oftheir similar chemical and physical properties as well as theirsimilarity in behavior in the brazing alloys herein described. I havefound that from 1 to l0 per cent of one or more of these metals may beadvantageously employed, but the total amount should not in generalexceed about 10 per cent. It is to be understood that small amounts ofstill other elements may be present in the alloys as impurities or asintentionally added ingredients without substantial adverse effect uponthe benecial properties of the alloys for brazing purposes. The alloyoompositions claimed hereinbelow are intended to permit the inclusion ofsuch minor alloying elements.

One of the advantages of having filler metal of`the kind hereindescribed which melts at a temperature close to that of the solutionheat treating temperature of the alloy being brazed, is that in somecases brazing and solution heat treatment may be carried outsimultaneously. In other instances where the member being brazed hasreceived a solution heat treatment, another exposure to the sametemperature only amounts to a repetition of a previous treatment andtherefore introduces no new factor in the treatment of the alloy.

Although the ller metal alloys described above are particularly adaptedto the brazing of solution heat treated aluminum base alloys, they arealso useful in joining members of aluminum or aluminum base alloys thatare not so treated.

The advantage gained through use of my alloysin such cases is that thejoining operation can be conducted at a lower temperature and with lessdanger of encountering difficulties sometimes attendant upon the use ofhigher brazing temperatures. The brazing alloys may also be employed inmaking joints between aluminum members and members of other metals orbetween nonaluminous metals.

In using the brazing alloy, suitable fluxes should be employed.Generally those fluxes which contain alkali metal halides aresatisfactory. Such fluxes adapted to brazing are now available and havebeen found to give satisfactory results.

As an illustration of the operation of my lnvention, I may cite anexample of the brazing of an assembly of aluminum alloy members. Themembers, composed of an alloy consisting of l 0.6 per cent magnesium,0.25 per cent chromium and balance aluminum and the usual impurities,were first cleaned with emery clothand carbon tetrachloride. The cleanedmembers were assembled in an inverted T position and filler metalcomposed of 62.1 per cent silver, 27.9 per cent aluminum, and 10 percent copper was placed along one side of the intersection. A suitablebrazing flux was painted on the areas where the joint was to be made.The entire assembly was then placed in a furnace and heated up toslightly below about 1000 F., the solution heat treating temperature forthe alloy members, and held at this temperature for a period of 5minutes. At the conclusion of this time the assembly was withdrawn fromthe furnace and cooled in an air blast. The filler metal was found tohave flowed to the other side of the T joint and to have formed asatisfactory fillet on both sides of the joint. The jointed members werefirmly attached to each other and the joint could only be ruptured withdifficulty when pulling the members apart under tension.

Although certain examples have been given hereinabove, it will beappreciated that other compositions coming within the scope of myinvention may be made and will give equally satisfactory results.

I claim:

l. A brazing alloy containing from about 56 to 70 per cent silver and 21to 31 per cent aluminum, the silver being in the proportion of 2 to 3parts to 1 part of aluminum, and from 7 to 16 per cent copper, saidalloy being characterized by having a melting point below 1000 F.

2. A brazing alloy composed of from about 56 to 70 per cent silver, 21to 31 per cent aluminum, the silver being in the proportion of 2 to 3parts to l part of aluminum, from 7 to 16 per cent copper, and from l to10 per cent of at least one of the metals of the group consisting ofantimony, lead, tin, and bismuth,`the total amount of said metals notexceeding 10 per cent, said alloy being characterizedby having a meltingpoint below 1000o F.

3. A brazing alloy containing from about 62 to 65 per cent silver andabout 26 to 27 per cent aluminum; the silver being in the proportion of2.4 parts to 1 part of aluminum, and from 8 to 12 per cent of copper,said alloy being characterized by having a melting point below 1000 F.

WALTER A. DEAN.

